1. Field of the Invention
The present invention relates to a three-dimensionally designed display radar which is carried, for example, on a ship and which preferably detects a target.
2. Description of the Related Art
In recent years, the radar is broadly utilized on a small ship such as a pleasure boat. As well-known in the art, such a radar is operated as follows. That is, a transmission radio wave, which is transmitted from a rotating antenna, is reflected by a target. A reflected radio wave therefrom is received to display a concentric circular image depicted about a center of its own position on a display unit.
In such a system, the intensity of the reflected radio wave is displayed as a difference in brightness of a point at which the target exists, for example, on a screen of the display unit of the raster scan type.
When such a radar is used, it is possible to observe an objective moving ship which approaches a subjective ship during its navigation and anchorage. Further, it is possible to monitor whether or not the subjective ship is deviated from an anchorage position, for example, due to a tide, on the basis of the reflected radio wave from a fixed reflecting object.
In general, when such a display unit equipped for the ship radar is operated, the target point on a screen is displayed in a two-dimensionally designed manner as in a plan view, in which the image is not displayed such that the target is displayed based on information on the height on the screen.
Therefore, for example, when the radar is carried on the pleasure boat or the like, it is difficult for a user who is not familiar with the radar observation so much to effectively perform the recognition and the observation of surrounding circumstances and the detection of the target on the basis of the displayed image. A problem arises in that the carried radar is hardly utilized in an effective manner.
In order to solve this problem, the present applicant has proposed a radar apparatus which enables a user who is not accustomed to the radar observation so much, for example, to effectively detect the target by three-dimensionally displaying the target on the screen of the display unit. Details of the three-dimensionally designed display radar are disclosed in Japanese Patent Publication No. 8-30732.
The three-dimensionally designed display radar comprises a radar transmitting/receiving unit for deriving, from a target, signals concerning the orientation information, the distance information, and the reception intensity information; a display unit; a three-dimensionally designed coordinate converter for making conversion into a signal to indicate the orientation information and the distance information as XY coordinate values based on the perspective projection drawing method added with the reception intensity information to indicate a length of a straight line as a height of the target; a marker-generating means for sending a lattice-shaped distance marker signal when three-dimensionally designed display is made on a screen of the display unit; and a storage means provided with storage addresses corresponding to respective picture elements on the display unit, for storing the reception intensity information in the storage address corresponding to the XY coordinate obtained by the three-dimensionally designed coordinate converter and storing the marker signal when the three-dimensionally designed display is made so that the stored information and the stored marker signal are successively read to send an image signal to the display unit.
The three-dimensionally designed display radar concerning the conventional technique enables an observer who is not accustomed to the radar observation so much to perform the detection or the like by three-dimensionally displaying the target on the display radar.
However, the conventional three-dimensionally designed display radar is constructed such that the two-dimensional display and the three-dimensionally designed display are switched to be selectively used. Therefore, at first, when the two-dimensional display screen is switched to the three-dimensionally designed display screen, or when the three-dimensionally designed display screen is inversely switched to the two-dimensional display screen, a certain period of time is required to allow the antenna to make one revolution. That is, in the case of an ordinary radar, a period of time of about 2.5 to 3 seconds is required. During this period, the user, for example, a navigator has to wait for the period of time.
Secondly, a certain term is required until a navigator, who is accustomed to the two-dimensional display screen, is accustomed to the three-dimensionally designed display screen. During the term until the navigator is accustomed, it is preferable that the two-dimensional display and the three-dimensionally designed display can be simultaneously used in combination. However, such an operation cannot be performed when the conventional three-dimensionally designed display radar is used.
Further, the conventional three-dimensionally designed display radar is constructed such that the lattice-shaped distance marker indication is superimposed on the display unit. However, when the radar is used during the navigation through a river or an inlet, the surrounding targets themselves have their shapes which are easily observable three-dimensionally in many cases. If the distance marker is displayed on the screen in the superimposed manner when the three-dimensionally designed image data is displayed, then the display is inversely complicated, and it is difficult to observe the image of the objective target in some cases.
Furthermore, the three-dimensionally designed display radar described above is constructed such that the three-dimensionally designed display is made on the basis of only a point of sight in a certain fixed direction. Therefore, the three-dimensionally designed display radar fails to satisfy the demand that the three-dimensionally designed display is intended to be made on the basis of a point of sight at an arbitrary angle.